performance loss

[pigeon laker]

I've been reading through this forum for awhile and learned alot about outboards,but really no solution to my problem.Motor is a 99 Merc 115,used to run great,would rip the rope from a skiers hands if i gave full throttle and was almost scary when at top speed.After the winter(was winterized at dealer)it has lost some power.Seems sluggish out of the hole and top end not near what it was.I have lost about 300-400 rpm's.Brought it into the shop and everything seems OK.compression is good,lots of spark and fuel to all cylinders.Mechanic says try a smaller prop,but that will not solve anything.I rebuilt the fuel pump,removed and cleaned the carbs,lync and sync,new fuel filter,still no help.As well,the bottom plug is alot cleaner than the rest.Almost like new,while the top 3 are quite black.Iswitched the plugs around and the dirty plug came clean in the bottom cylinder.I can't think of anything else but the bleed system.How do you check it?By the way,I was getting about 5000 rpms before and now down to 4600.I know this is a really long post but I might as well ask all my questions at once.I also ran a can of seafoam mixed with 3/4 gals of gas through it,no difference,but I did notice the rpms jumped quite a bit as the small gas can was running out.That is why I am suspicious of the bleed system and thinking the bottom cylinder is flooding.Thanks in advance.

 

[westexasrepublic]

Re: performance loss

if the bottom plug is clean compared to the others its not firing. So how did you confirm all cylinders are getting fuel AND have spark? or are you just going by a mechanics word?

 

[pigeon laker]

Re: performance loss

Just took the mechanic's word for it

 

[backyard mechanic]

Re: performance loss

Assuming your mechanic is a good one- Let me ask a few questions. Is this the first you've had ethanol fuel in the tank? Is it possible your tank is plastic? Explore those things and you may find the problem.

I had an depreciation of performance (equal to yours) in my 95 115 merc 2 stroke after it was set up correctly but it was contributed to ethanol fuel. Switching back to REAL gas was the answer.

I know my mechanic real well (it's me) and yes, I am beyond positive that the motor is set up 100% correct. Mind you; I purchased this boat/motor package just after it had been "tuned up". It didn't run for crap so I went through it and found every adjustment out of sync. I also found a coil bad and not too long after my stator went south. She runs like a dream now. The previous owner said it never ran that good when he had it. (PS: He had it in to the same mechanic every year for maintenance and tune ups.)

My point here is this; get yourself a manual and you be the double checker... YOU be sure the motor is set up correctly. If the carbs, oil injection and timing is set/sync'd properly it will perform well PROVIDED all is working well. Case in point; black plugs would indicate over fueling or lack of spark, therefore something is not right.

 

[EvinrudeMasterTech]

Re: performance loss

If that bottom cyl IS firing and has compression, then its probably either pulling air or water. You may have blown a takedown gasket (gasket between the block and midsection) or a water jacket / exhaust housing gasket. Has the motor ever been overheated? Even momentarily?

 

[pigeon laker]

Re: performance loss

Yes it was overheated once,but ran perfectly for the rest of the season.I'm still thinking the bleed system as to fuel pooling in the lowest cylinder if an injector nozzle being plugged or check valve not working right.

 

[EvinrudeMasterTech]

Re: performance loss

What do your spark plugs look like, particularly on #6?

 

[sschefer]

Re: performance loss

Oil pooling in the bottom cylinder can be from bad crankshaft seals. On some engines these seals are o-rings and on some they are simply a set of steel rings between the main bearing rollers. The steel ring type will leakdown oil from the other cylinders when the engine is shut off and sits for a while. This oil normally gets sent up to the upper main bearing when the engine is restarted. If it doesn't get cleared from the cylinder it will cause that cylinder to run lean, heat up and loose power but only while the engine is first started. It should burn off within the first five minutes if the spark is normal and the plug is strong.

Do a vacuum test on the crankcase and see if its within spec's. This test is also known as a primary compression test.

 

[wobiii]

Re: performance loss

Did you ever get this problem fixed? I am having a similar problem with a 2005 merc 115. Just changed the plugs recently and didn't notice any real difference in the 4.

 

[pigeon laker]

Re: performance loss

Not fixed,at least at the end of last season.I haven't even started it this year ,but,after doing some research on this site I read about a bad exhaust divider plate gasket.When I removed the divider plate the gasket was in very poor condition.I could have done the damage removing the divider plate,but,it came off quite easily.I'm waiting on thegasket(back order) and will be posting the results after the repair is done.If you decide to change yours could you post your results.